1. Field of the Invention
This invention relates generally to a method to precisely measure electrical parameters in integrated circuits in a semiconductor device. More specifically, this invention relates to a method to precisely measure electrical parameters in integrated circuits in a face down semiconductor device.
2. Discussion of the Related Art
The solder-bump flip-chip interconnection technology was initiated in the early 1960s to eliminate the expense, unreliability, and low productivity of manual wirebonding. The flip-chip or controlled-collapse-chip connection (C.sup.4 or C4) technology utilizes solder bumps deposited on wettable metal terminals on the chip and joined to a matching footprint of solder wettable terminals on the substrate. The upside-down chip (flip-chip or face down chip) is aligned to the substrate, and all joints are made simultaneously by reflowing the solder.
Semiconductor die are subjected to two basic sets of test procedures. The first set of test procedures is conducted while the die are still in wafer form and the second set of test procedures is conducted after the die have been separated and have been packaged. Test procedures have been developed for the testing and analysis of semiconductor die that are packaged face up. Because the face of the semiconductor die is facing down in a flip-chip, the face is unavailable for the test procedures developed for the more conventional face up semiconductor die.
Historically, one of the primary integrated circuit tools for electrical waveform analysis at the small micron to sub-micron level is the "electron beam microprobe." The electron-beam microprobe is a specialized scanning electron microscope (SEM) configured to provide a visual image of integrated circuits on a die, with or without voltage contrast. Voltage contrast is available when the integrated circuits are electrically activated. The electron beam microprobes are navigated to specific nodes in the integrated circuit on the semiconductor die based upon a computer database containing the actual physical layout of the integrated circuit on the semiconductor die. Once a node in the integrated circuit that is to be tested is located, the electron beam is aimed at a specific conductive pattern on the die and senses what the electrical potential is at the node. Further actual electrical test patterns can be used to stimulate the device under test and the electron-beam's secondary electrons can be used to observe waveforms and timing patterns in the integrated circuit on the die. This capability is crucial during the debugging portion of the development phase of a new integrated circuit design and is a key tool to examine production test units and integrated circuits returned from field use. In order for an electron beam microprobe measurement system to work, the electron beam microprobe is best placed on a conductive interconnect line although alternating current (ac) charge can be sensed through a thickness of thousands of Angstroms (.ANG.) of dielectric. However, the measurement conducted through dielectric having a significant thickness is not sufficiently accurate for precise determination of the electrical parameters of the integrated circuit.
Because the face of the flip-chip is facing down and is close to the packaging substrate, the conductive interconnect lines of the flip-chip are unavailable for the standard electron beam measurements.
Therefore, what is needed is a method of measuring electrical parameters of the face down semiconductor device from the backside of the semiconductor device using elements of the semiconductor device that are available for electron beam microprobe analysis.